The invention relates to a hydraulic safety brake valve arrangement for a motor which is actuatable by a control valve and which can be loaded in at least one operating direction by an external force, comprising a main valve which, in the rest position, closes at least that motor conduit which serves as an outlet conduit in this operating direction, opens under the influence of the presssure at the connection on the pump side and thereby forms a first throttling point in the supply motor conduit and a second throttling point in the delivery motor conduit, the openings of both throttling points changing in the same sense and depending on the flow through the first throttling point at least during braking operation.
In a known arrangement of this kind (DE-OS 32 25 132), the slide of the main valve comprises two control edges which, in conjunction with two annular grooves, form the first and second throttling points. The slide is loaded at one end by the pressure at the connection on the pump side and at the other end by a spring and by the pressure at the connection of the first throttling point on the motor side. The spring holds the pressure drop at the first throttling point constant. The slide position thereby depends on the quantity. Since the main valve closes both motor conduits in the rest position and can be directly connected to the motor housing, it is ensured that, if there is a fracture in the hydraulic conduits, the liquid volume in the motor is kept shut. Since the opening of the second throttling point depends on the amount of flow through the first throttling point, the quantity delivered by the motor is also limited. This results in a braking effect that reduces the influence of the external force. However, with a given opening of the second throttling point, the quantity delivered depends on the external force. This is often undesirable because, for safety reasons, a particular deceleration must not be exceeded. This applies, for example, to all hydraulically actuated consumers subjected to preloading, such as cranes, excavators, lifts or like equipment, irrespective of whether their motor is a rotating or a linear motor. It is also disadvantageous that the first and second throttles are operative not only during braking operation but also during normal operation and therefore give rise to additional throttling losses.